Cloudflare is taking over tsrs, a port of the TypeScript compiler to Rust. The company says it checks types up to eight times faster than TypeScript 7.0 and uses 70% less memory. It will be developed inside Oxc, the Rust-based JavaScript toolchain from VoidZero, the team Cloudflare bought this summer.

The company repeats one message several times: this is not a fork. Microsoft still steers the language, and the teams share what they find. Cloudflare engineering director Christoph Nakazawa says that, as a result, TypeScript 7.1 is already about 2.5 times faster. Microsoft shipped the 7.1 beta the same day.

Where tsrs came from

The project started a month ago at Owner.com, a company that builds software for restaurants. Its backend has 37,000 TypeScript files, and the Go compiler took 19 GiB of memory and 80 seconds for a single check. When several AI agents work in parallel and each wants to verify its own changes, numbers like that become a ceiling.

Max Schwenk, who leads AI developer experience there, had Claude Opus 5.5 rewrite the compiler in Rust while he only set tasks and judged the output. More than twenty subagents ran in parallel, and by morning there was a working type checker. Type checking in Owner.com's CI now takes about seven seconds. “I wrote zero code,” Schwenk says.

Why Rust when Go already exists

Microsoft rewrote the compiler in Go for TypeScript 7.0 and got roughly a tenfold speedup. Cloudflare's interest in Rust is about WebAssembly: Go brings its garbage collector into Wasm, while Rust gives direct control over memory. That makes it easier to run a full development environment in a browser or in an isolated Workers sandbox, where agents write and build apps.

How they check it gets things right

A fast compiler is useless if it catches fewer errors. tsrs runs against TypeScript's official conformance tests, gets errors deliberately injected into real projects, and has its memory handling checked with Miri. That has already caught a bug that only showed up in an optimised build. Some differences from upstream remain, such as the order in which diagnostics are printed.

Our take

For anyone building sites in TypeScript, the practical upshot is that builds and type checks will get noticeably faster, most likely in TypeScript 7.1 itself, with no change of tools. It is too early to put tsrs into a production pipeline. But the pattern of a person setting the task and checking it while agents write the code is already working at this scale. Details are in The New Stack.